Re: [Patch, fortran] 99307 - FAIL: gfortran.dg/class_assign_4.f90 execution test

[Tobias Burnus <tobias@codesourcery.com>]

Hi all,

as preremark I want to note that the testcase class_assign_4.f90
was added for PR83118/PR96012 (fixes problems in handling class objects, Dec 18, 2020)
and got revised for PR99124 (class defined operators, Feb 23, 2021).
Both patches were then also applied to GCC 9 and 10.

On 26.03.21 17:30, Paul Richard Thomas via Gcc-patches wrote:
> This patch comes in two versions: submit.diff with Change.Logs or
> submit2.diff with Change2.Logs.
> The first fixes the problem by changing array temporaries from class
> expressions into class temporaries. This permits the use of
> gfc_get_class_from_expr to obtain the vptr for these temporaries and all
> the good things that come with that when handling dynamic types. The second
> part of the fix is to use the array element length from the class
> descriptor, when reallocating on assignment. This is needed because the
> vptr is being set too early. I will set about trying to track down why this
> is happening and fix it after release.
>
> The second version does the same as the first but puts in place a load of
> tidying up that is permitted by the fix to class array temporaries.

> I couldn't readily see how to prepare a testcase - ideas?
> Both regtest on FC33/x86_64. The first was tested by Dominique (see the
> PR). OK for master?

Typo – underscore-'c' should be a dot-'c' – both changelog files

>       * trans-expr_c (gfc_trans_scalar_assign): Make use of pre and

I think the second longer version is nicer in general, but at least for
GCC 9/GCC10 the first version is simpler and, hence, less error prone.

As you only ask about mainline, I would prefer the second one.

However, I am not happy about gfc_find_and_cut_at_last_class_ref:

> + of refs following. If ts is non-null the cut is at the class entity
> + or component that is followed by an array reference, which is not +
> an element. */ ... + + if (ts) + { + if (e->symtree + &&
> e->symtree->n.sym->ts.type == BT_CLASS) + *ts =
> &e->symtree->n.sym->ts; + else + *ts = NULL; + } + for (ref = e->ref;
> ref; ref = ref->next) { + if (ts && ref->type == REF_COMPONENT + &&
> ref->u.c.component->ts.type == BT_CLASS + && ref->next &&
> ref->next->type == REF_COMPONENT + && strcmp
> (ref->next->u.c.component->name, "_data") == 0 + && ref->next->next +
> && ref->next->next->type == REF_ARRAY + && ref->next->next->u.ar.type
> != AR_ELEMENT) + { + *ts = &ref->u.c.component->ts; + class_ref = ref;
> + break; + } + + if (ts && *ts == NULL) + return NULL; +
Namely, if there is:
   type1%array_class2 → array_class2 is used for 'ts' and later (ok)
   type1%type%array_class2 → NULL is returned  (why?)
   class1%type%array_class2 → ts = class1 but array2_class is used later on (ups!)
   class1%...%scalar_class2 → ts = class1 but scalar_class2 is used
etc.

Thus this either needs to be cleaned up (separate 'ref' loop for
ts != NULL) – including the wording in the description which tells what
happens if 'ts' is passed as arg but the expr has rank == 0 – and
what value is assigned to 'ts'. (You can then also fix 'class.c::' to
'class.c: ' in the description above the function.)

Alternatively, you can leave the current code ref handling code in place
at build_class_array_ref, which might be the simpler alternative.

Otherwise, it looks sensible to me.

Tobias

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